1. Field of the Invention
This invention relates to a method and apparatus for controlling the flow of process fluids and, more particularly, to a system for feeding process water in a controlled manner through a primary loop and secondary loops.
2. Description of the Background Art
In the field of flow control systems, one technique for providing chilled process water to a plurality of remote sites is to use a primary flow loop from chillers to the sites where the water is to be utilized, as for air cooling, and then back to the chillers for recycling in a continuous cycle of operation. At the remote sites where the process water is to be used, secondary pumped flow loops tap from, and return to, the primary loop, the chilled water for use in air cooling at each of the various sites. As a result, there is one primary loop in a continuous flow and a plurality of pumped secondary loops for utilizing the water from the primary loop as needed.
In considering any one secondary loop, there will be a section of crossover line which is common with both the primary loop and the secondary loop. The apparatus coupling the primary loop with a secondary loop is a water bridge. A primary pump is used to continuously feed the water through the primary loop. A secondary pump is used to feed the water through each secondary loop but only at a given rate and only when required. Without appropriate controls, however, the system would be very inefficient, chilling and/or feeding more or less water than is needed for the intended air cooling.
In U.S. Pat. No. 3,729,051, the problem of controlling the quantity of flowing water was addressed and solved. According to that patent, a small supplemental water line is placed across the common extent of the primary and each secondary loop. The supplemental line at each secondary loop was of a significantly smaller diameter for a limited flow, merely sufficient to sense a primary flow balance between the primary loop and the flow of the secondary loop.
For optimum efficiency, the flow through the primary loop should equal the flow required to supply the primary flow needs to the total of secondary loops. If insufficient water is pumped in either loop, the intended cooling will not be effected. If excess water is pumped, unnecessary energy will be expended in moving the water. By sensing the flow along the supplemental line, verification may be made that water is flowing and that pressure exists in a supplemental line. So long as the sensed water in the supplemental line remains at the optimum predetermined flow, no change is made to the fluid flow. If, however, the sensed water varies from the predetermined flow, a signal is sent back to a first control valve in the primary loop to restrict the flow and thereby minimize the work done by the pump of the primary loop. This effects a greater efficiency.
In a subsequent improvement, as described in U.S. Pat. No. 3,875,995, temperature is also taken into account for controlling water flow. In the event that the supply or return water in the secondary loop varies from its intended, predetermined temperature, inefficiency results. If the temperature of the water in the secondary loop is not cool enough, the intended air cooling will not be effected. If the temperature of the water in the secondary loop is too cool, excess chilling is being done at an unnecessary cost to the system and its user. As a result, a temperature control sensor is provided. So long as the sensed temperature is at a predetermined value, the chilling simply continues. If, however, the temperature deviates from the predetermined value, the difference is sensed and a signal is sent to a second control valve located in the crossover line of the water bridge to vary the quantity of chilled water provided to the secondary loop to temperature demand of the loop. This feature further increases the efficiency of the system by reducing the primary water to a minimum.
In a further improvement to fluid control systems, as described in the copyrighted BRDG-TNDR Corporation brochure of 1988, the signals generated for temperature and pressure control are fed back from the water bridges of the air cooling subassemblies to the water chiller subassembly to vary the amount of recirculating water being fed through the chiller to thereby modify the temperature and pressure of the water in the primary loop.
A further improvement is described in U.S. Pat. NO. 5,089,975. In its simplest terms, the temperature and flow sensors are replaced with electronic sensors of a size and capability more efficient than those previously known and utilized. Their use generates more accurate readings, and they have less adverse effect on the flow. This further increases the accuracy of readings and provides greater control and efficiency in the system. In addition, each controller is removed from the site of sensing and repositioned in a common electronics package. As such, all electronic controls for each secondary loop are integrated into a common controller for greater overall efficiency. This more readily allows all the controllers for all the secondary loops to be in two-way communication with each other and/or a common host computer for integration of the system. As such, the efficiencies effected to the system are greater than the sum of the efficiencies of the individual water bridges.
A further improvement is described in U.S. Pat. No. 5,138,845. According to that disclosure, sensor means are provided at each water bridge to determine the operating characteristics of the system, present and historical, and to integrate such information at a master controller for modifying the operating characteristics of the control mechanisms at the various individual water bridges.
As referred to above, the prior art discloses systems for controlling the flow of process fluids. Nothing in the prior art, however, controls the flow with the simplicity, accuracy and efficiency afforded by the present invention.
Therefore, it is an object of this invention to provide a method and apparatus which overcomes the aforementioned shortcomings and which is a significant contribution to the advancement of the arts.
It is a further object of the present invention to control the limits of openness of one of the valves of any water bridge as a function of the extent of openness of the other of the valves at such water bridge.
It is a further object of the present invention to control each site of a water bridge system independently of all other sites of such system.
It is an object of the present invention to employ at each water bridge of a system, a common control with a first component coupling a first sensor and valve, a second component coupling a second sensor and second valve, and a supplemental component to couple the first and second components to vary the operation of the first and second components, as a function of the specific application of the system.
Lastly, it is an object of the present invention to provide an improved method and apparatus for coupling a primary loop with a secondary loop for circulating processing fluids therebetween comprising in combination a first connection for the feed line of the primary loop and a second connection for the return line of the primary loop; a third connection for the feed line of the secondary loop and a fourth connection for the return line of the secondary loop: a crossover line coupling the four connections; first valve means for controlling the flow through the primary loop; first sensor means responsive to the flow across the crossover line to control the first valve means; second valve means in the path of flow through the crossover line; second sensor means responsive to the temperature of the process fluid in the secondary loop to control the second valve means; a common controller for the first and second sensor means adapted to control the first and second valve means as a function of the sensed temperature and flow; and a common controller for the first and second sensor means adapted to control the first and second valve means as a function of the sensed flow and temperature with means to limit the extent of opening of one of the valve means as a function of the extent of opening of the other of the valve means.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.